1. Field of the Invention
The present invention relates to a label printer. More specifically, the invention relates to a label printer which prints article name together with data such as weight, rate, price, preparation date, effective date, tare, article number and bar code on a label to be applied to products or packaged products. Otherwise only article name is printed on it. It is used in connection or installation with electronic balances such as a weight balance, a digital balance or a price indicating balance and a packing machine with price indication in supermarkets or it is used separately.
2. Description of the Prior Art
In conventional label printers, impact print system is adopted where printing is carried out by application of impact to a printing surface using a magnet, a hammer or the like. When characters of an article name are to be applied to a label made by such printers, separate printing means such as a rubber stamp or printers with different types of characters must be used. Such printers therefore are disadvantageous in that (1) when articles of a new name are sold a new rubber stamp must be used, (2) hands may be soiled by ink, and (3) supply of ink is required and the maintenance work is troublesome.
In order to eliminate above mentioned disadvantages, various printers of dot print type without impact print have been recently developed, which have the advantages that the treatment is simple, the maintenance is not troublesome, and any characters or symbols may be printed.
Conventional label printers have display field for weight, rate, price of articles but not display field for article names.
In conventional label printers, preparation date of articles as well as effective date (date after which product is no longer in the case of foods) must be printed by previously setting the dates using corresponding dial switches. Setting of date must be renewed every day. If the date renewal were forgotten carelessly, an unfavorable condition would occur in that really fresh articles would appear to purchasers to be old.
In conventional label printers, use of printers of heat senitive type, electric discharge type, wire dot type, ink jet type or the like is proposed where characters or symbols are designated by a number of dots. When printing is carried out on a label using such printers, required characters, numerals, symbols or bar codes are printed with the print head and the label in relative motion, for example, the label is logitudinally moved with respect to the laterally aligned print head. When one print heads, e.g. that printing a bar code on a label, does not work, omission of print in a corresponding portion may cause false designation of codes or other information. Such wrong operation of a print head cannot be discovered readily. In the case of bar code, for example, the wrong operation cannot be determined until values read in the bar code reader are compared.
In order to check operation of each print head, all print heads are simultaneously operated and printing is carried out throughout the whole label surface. If omission of printing occurs in any portion during the above mentioned operation, the portion corresponding to the omission remains the color of the original paper thereby wrong operation of a print head is determined. When the above mentioned checking method is applied to printers such as a thermal printer with a number of print heads arranged in a lateral line, however, since power supply capacity for heating is set (rated) corresponding to part (e.g. a half) of all print heads so as to make the printer compact, particular power supply capacity for the checking inevitably makes the printer larger.
In conventional label printers, the control system is generally provided with accumulator memory in which weight, price, number or the like of articles are summed and accumulated per article item.
In such label printers, however, when a label is not properly held in a label holder on account of wrong operation of the label feed or when feeding operation is carried out at wrong article code, the label is printed with undesired data. Efficiency of princing operation in this state is decreased because additional work is necessary to detect the undesired data and to correct the wrong data.
In conventional label printers generally, labels are applied to a label carrying paper formed in a band and spaced at prescribed intervals along it. The label carrying paper is moved intermittently in a certain direction and stopped at a prescribed position opposite to the print head for printing. When the label travel length is specified only as a stroke length, the stopping position is shifted at occurrence of a slip in the label feeding whereby information is not printed at a specified position of the label.
In conventional practice, a label position detecting unit is installed at the moving path of labels to detect the label position. By stopping the label feeding when the detecting unit detects the label to proper position, each label is printed securely at a prescribed position.
Above mentioned conventional label position detecting unit is composed of a detector comprising a light emitting element and a light receiving element, and of a comparator comparing the detector output voltage with the previously set reference voltage and determining from the voltage difference either the label is at the detecting position of the detector. The light emitting and receiving elements are opposite to each other and the label carrying paper is interposed between both elements. As labels are conveyed, light from the light emitting element is received by the light receiving element through only carrying paper or through both the carrying paper and the label. The reference voltage is set to a prescribed voltage between the high output voltage of the detector during detection of the label applied gap and the low output voltage during detection of the label using electric resistance division or programming method.
Since change of the label carrying paper in material and thickness changes the light permeability, the reference voltage must be set every time when the label is changed or a new label carrying paper is used. Omission of the renewal setting of the reference voltage may cause the frequent occurrence of defective labels and the wrong operation of printers. Accordingly, improvement in this respect has been desired.